1. Field of the Invention
The present invention relates to an ink jet head and an ink jet recording apparatus that prints by discharging ink droplets through nozzle apertures, and to a method for removing unwanted substances including dust particles and bubbles from the ink jet head.
2. Description of the Related Art
There is known a conventional ink jet recording apparatus that records characters and images on a recording medium by using an ink jet head having a plurality of nozzles for discharging ink. In this ink jet recording apparatus, the nozzles of the ink jet head are formed in a head holder in such a position as to face the recording medium. The head holder is mounted on a carriage and performs scanning in a direction perpendicular to a transport direction of the recording medium.
FIG. 7 is an exploded schematic diagram showing an example of such an ink jet head. As shown in FIG. 7, a plurality of grooves 102 are formed in parallel in a piezo-ceramic plate 101, and the grooves 102 are separated by side walls 103. One end portion of each groove 102 in the longitudinal direction extends up to one end face of the piezo-ceramic plate 101, whereas the other end portion of each groove 102 does not extend up to the other end face of the piezo-ceramic plate 101 and gradually decreases in depth. Electrodes 105 for applying drive voltages are formed in the opening-side surfaces of both side walls 103 of each groove 102 so as to extend in the longitudinal direction thereof.
An ink chamber forming substrate 107, which forms an ink chamber 106 communicating with the end portion of each groove 102 where the depth is decreased, is joined to the piezo-ceramic plate 101 on the side where the grooves 102 are opened. Further, a passage forming member 109, which seals one side of the ink chamber 106 and has an ink supply passage 108 for supplying ink to the ink chamber 106, is fixed to the ink chamber forming substrate 107.
A nozzle plate 110 is joined to the end face of the joined body of the piezo-ceramic plate 101 and the ink chamber forming substrate 107 on the side where the grooves 102 are opened. Nozzle apertures 111 are formed in the nozzle plate 110 in such positions as to face the respective grooves 102 of the nozzle plate 110.
In the recording head that is constructed in the above-mentioned manner, when the ink is supplied to the grooves 102 via the ink supply passage 10 and predetermined driving electric fields are applied to both side walls 103 of a predetermined groove 102 through the electrodes 105, the side walls 103 are deformed to change the capacity of the predetermined groove 102 so that the ink can be discharged from the groove 102 through the nozzle aperture 111.
The above-described ink jet head is disadvantageous because the ink cannot be satisfactorily discharged due to dust, bubbles, etc. in the ink. To address this problem, a filter 112 is usually provided at the end of the ink supply passage 108 by the side of the ink chamber 106 so as to prevent dust and bubbles in the ink from entering the ink chamber 106.
Although the use of the filter 112 can prevent the entry of dust and bubbles of a certain size, it is difficult to completely prevent the entry of dust and bubbles. Although the use of a finely meshed filter would prevent the entry of dust to a larger degree, such a filter disturbs the flow of ink. It is therefore impossible to use a finely meshed filter.
Dust which passes through the filter 112 is removed by a so-called cleaning operation in which the ink contained in the grooves 102 and the ink chamber 106 is absorbed through the nozzle apertures 111. This cleaning operation, however, cannot completely remove the dust. The head from which the dust has not been removed must be disposed of.